The present invention relates to a method for equalization of metal surfaces, especially the equalization of metals to enable cleaning of the surface of a substrate member to be soldered at a low cost.
In order to obtain a good condition for a soldering junction, it is necessary to mutually diffuse atoms between a material for connection or a material to be connected (or to be soldered) (hereinafter referred to as a substrate member) and a solder. In addition, for obtaining an excellent spreadability of a solder, it is important to offer a sufficient amount of heat as well as to clean the surface of a substrate member.
For this purpose, a method for removing oxides from the surface of a substrate member prior to soldering has been adopted. The method involves a chemical reaction using an organic acid having a reducing power, namely a so-called fluxing agent.
In the case where the removal of contamination can not be accomplished by a chemical reaction using a fluxing agent only, a method of removing oxides from the surface using an acid such as hydrochloric acid, such or sulfuric acid, ammonium persulfate, selected in accordance with the kind of the substrate member, or a method for mechanically removing the contamination using sandpaper, a brush or the like, are generally adopted.
There has been known a method (grazing) for obtaining a material composed of a superfine homogenous structure or an amorphous structure excellent in corrosion resistance, abrasion resistance, etc. by rapidly scanning laser beams to a metal material. A steel material, carbide or the like is proposed. This grazing method is considered to be applicable for treating a metallic material (for example a material for a turbine engine or a turbo-charger of an automobile) which is to be exposed to a high temperature atmosphere under a high pressure.
The working method using laser beams is explained in "ZOKU.multidot.LASER KAKOH (Continuation Laser Working)" p. 164 (written by Akira Kobayashi, published by KAIHATSUSHA) for instance. Other publications relating to this kind of technology are available in Japanese Patent Unexamined Publication Nos. 63-97382, 62-256961, etc..
In the prior arts abovementioned, the substrate member is chemically treated with an acid or the like before soldering. In this regard, it is necessary to sufficiently clarify the surface of the substrate member in advance of soldering. There is, however, the problem that the potential of corrosion is usually high due to the remaining acid.
It is also necessary to dry the surface of the substrate member after washing it with water. In this washing step, the surface of the substrate member is likely to be reoxidized.
Said chemical method exhibits an effect to remove oxides and contaminants from the surface of the substrate member. However, it can not be expected to reform the surface of the substrate member for improving the wettability to a solder or to make the surface into the state excellent in resistance to oxidation. Besides, a poor condition between a plated layer and a base can not be improved or taken out, although the surface condition of the plating layer or the like is cleaned. Furthermore, facilities requiring a large amount of investment and a large number of treating steps are necessary to actually carry out the aforementioned method.